Addressing common misconceptions about radiant cooling
Covering ideal climates and designs.
By Saeed Danesh
300,000 feet of RAUPEX pipe was installed in the University of Chicago Campus North Residence Commons. The temperature of the student living quarters is maintained via REHAU in-slab hydronic radiant heated and cooling. IMAGE COURTESY OF Susan Kirt Photography LLC
One of the most persistent misconceptions about radiant cooling is that it inherently leads to condensation problems and that it can't be used in humid climates. However, with the right design and control strategies, radiant systems can operate reliably and efficiently, even in high-humidity regions.
Radiant cooling systems function by absorbing heat from a room primarily through radiation and some convection. However, unlike all-air systems, they do not handle latent (moisture) loads, that’s why they are often part of Hybrid Systems, most often paired with a Dedicated Outdoor Air System (DOAS). The DOAS addresses latent load, controls humidity, and meets fresh air requirements per ASHRAE Standard 62.1.
Condensation forms when a chilled surface drops below the dew point. The key to preventing this is to ensure that all radiant surfaces always stay above the space’s dew point. This is not a limitation of the climate, it’s a matter of design and control.
Four Key Strategies to Mitigate Condensation Risk
1. Tight Building Envelope
Preventing warm, moist outdoor air from leaking into the building is the first line of defense. A well-sealed envelope reduces unpredictable humidity loads and supports more stable indoor conditions.
2. Dew Point Based Control Strategy
Demand based control with dew point monitoring is essential. Sensors should monitor both temperature and humidity, allowing chilled water temperatures to adjust dynamically and keep surfaces safely above dew point.
3. Safe Surface Temperatures
ASHRAE Standard 55 recommends keeping radiant surface temperatures above 66°F (19°C) for cooling. Staying in this range ensures comfort and avoids surface-level condensation, while still delivering effective cooling.
4. Maintain a Dew Point Buffer
A simple, effective rule: supply water temperatures should be at least 3°F (or ~1.5°C) above the space’s dew point. This safety margin allows the system to operate without risking condensation, even during temporary spikes in humidity.
Radiant cooling system efficiency at a glance
Beyond condensation, radiant cooling is also widely misunderstood in terms of its efficiency and controllability. These systems often outperform traditional cooling methods in both energy efficiency and comfort, especially when integrated into a well-coordinated HVAC design.
A New Buildings Institute research study of site energy use in 23 radiant buildings found: Radiant buildings are more energy efficient than 90% of comparable buildings, with 2/3 receiving an EnergyStar score of 90 or above.*
Radiant cooling can operate at higher chilled water temperatures; typically, 55–60°F (13–16°C) versus 42–45°F (5–7°C) in conventional air systems. This translates to less chiller energy required for cooling. In some designs cooling tower temperatures are enough to supply the radiant systems. Bonus: A great match for heat pumps which make radiant systems a great choice supporting electrification goals and increasing LEED potential for Optimize Energy Performance.
49,000 feet of RAUPEX pipe was installed in the University of Washington Life Sciences Building. Because of the high solar gains of floor-to-ceiling windows, the radiant system was installed in the concrete slab on the southern and northwestern sides of the building, primarily for main entrances, lobbies, coffee shops, seating areas, professors’ offices and graduate student work areas. image COURTESY of Kevin Scott.
Additionally, radiant systems reduce or eliminate the need for large volumes of cooled air to be pushed through ductwork. This leads to significant reductions in fan energy, which can account for up to 25% of a building’s total electricity use. Bonus: Smaller ducts mean more architectural freedom. This also helps earn LEED and WELL points for Daylighting and View.
Ventilation and humidity control are still needed, but sensible loads are significantly reduced with radiant cooling. That means smaller ductwork, AHUs, and cooling coils. In many cases, a compact DOAS is sufficient to handle both ventilation and latent loads, resulting in lower equipment footprint, reduced energy use and easier maintenance.
Thermal mass and “Slow Response” can be a benefit. Thermal mass allows buildings to maintain comfort over time with minimal system cycling, reducing peak load demands and energy use. It also helps align cooling operation with off-peak hours or renewable energy availability. Bonus: Helps with grid harmonization and renewable energy use, contributing to LEED and electrification goals.
Smart design, smarter performance
Radiant cooling systems offer not just energy efficiency, but also exceptional zoning and control flexibility. Each zone can be independently managed using thermostats, actuators, and sensors that respond to occupancy, internal heat gains, and usage schedules.
This zoning capability allows for precise temperature control across different areas. By decoupling fresh air and cooling demand, when integrated into hybrid systems, it helps enhance occupant comfort and avoid energy waste. These systems adapt easily to dynamic conditions, whether it’s a classroom full of students during the day, an office with shifting peak hours, or a multi-use space with variable occupancy.
Advanced controls also allow for system optimization over time, adjusting water temperatures, flow rates, and sequencing based on real-time building data. This makes radiant systems ideal for smart buildings, schools, offices, and any high-performance project prioritizing comfort, flexibility, and long-term efficiency.
Rethinking radiant cooling
Radiant cooling is not limited to dry climates or niche applications. With a proper design, it becomes a versatile and energy-efficient solution suitable for a broad range of commercial and institutional buildings. With strategies to avoid condensation, proven energy performance and high comfort levels, radiant cooling systems offer various benefits that traditional systems can’t easily match. As electrification and decarbonization goals continue to shape building design, radiant cooling is well-positioned to be a part of that future.
* Energy Use, Occupant Surveys and Case Study Summary: Radiant Cooling and Heating in Commercial Buildings, New Buildings Institute and Center for the Built Environment, 2017